Cathode ray tube

ABSTRACT

A thin cathode ray tube. A low voltage is applied to a beam of electrons produced by an electron gun. The electron beam is electromagnetically deflected through a large angle. Four static deflectors are used to deflect and accelerate the beam of electrons, and to let the beam of electrons have a sufficient energy level when it reaches a fluorescent screen. The cathode ray tube can effectively increase the deflection angle of the beam of electrons and reduce an incident angle of the beam of electrons so as to reproduce an image with less distortion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cathode ray tube, and more particularly to acathode ray tube in which a beam of electrons is deflected by anelectromagnetic deflector and a static deflector.

2. Description of the Related Art

As shown in FIG. 6 of the accompanying drawings, a cathode ray tube is aglass bulb having a panel 1 and a funnel 2. A beam of electrons isproduced by an electron 5 gun 4 located in the neck 3 of the funnel 2and deflected by a deflection yoke 7 near a cone 6 of the funnel 2. Thebeam of electrons 5 is then focused onto a fluorescent screen layer 8inside the panel 1 and is scanned so as to reproduce an image.

A television receiver is required to be compact and thin. However, thetelevision receiver is also required to have a large display screen. Itis therefore essential to make the cathode ray tube as thin as possible.One approach for this purpose is to enlarge a maximum deflection angleof the electron beam. This approach will be described with reference toFIG. 7. As described above, an electron gun 4 produces a beam ofelectrons, a direction of which is changed by a deflection yoke 7 whilethe electron beam passes through a magnetic field generated by the yoke7. An angle by which the electron beam is redirected is called the"angle of deflection". When the electron beam is scanned at a peripheryof a fluorescent screen, it has a maximum deflection angle. The lengthof the cathode ray tube depends upon the maximum deflection angle of theelectron beam. Specifically, when the display screen has a height 2S,the electron beam 5 from the electron gun 4 is deflected at a deflectionpoint 0 with an angle θ. It is assumed that the electron beam has adeflection angle θ₀ (maximum deflection angle) at the periphery of thedisplay screen. An overall length of the cathode ray tube, F, isexpressed as follows:

    F=T+L+M+G

    L=S/tan θ.sub.0

where L represents a length between the deflection point 0 and thedisplay screen , M a length between the deflection point 0 and theforward edge of the electron gun 4, G a length of the electron gun, andT a thickness of the panel. According to this formula, L can be reducedby enlarging the maximum deflection angle θ₀, which means a reduction inthe length of the cathode ray tube. Table 1 shows a relationship betweenthe deflection angles and the entire length F of a 37-inch cathode raytube as an example.

                  TABLE 1                                                         ______________________________________                                        (Max. deflec. angle Θ.sub.0) × 2                                                     Whole length F                                             ______________________________________                                         90°        1090 mm                                                    110°        810 mm                                                     130°        590 mm                                                     150°        440 mm                                                     ______________________________________                                    

where T+M+G=150 mm.

The larger the maximum deflection angle, the shorter the cathode raytube as a whole. However, it is necessary to raise the level of energyapplied to the deflection yoke and intensify the electric field to begenerated when the deflection angle is made as large as possible whilekeeping the electron beam at a predetermined energy level. For thispurpose, an electromagnetic deflector having a high output level shouldbe used, which means a possible increase in the size of the televisionreceiver and in power consumption.

Further when deflection angle is large, the electron beam will beradiated onto the fluorescent screen 8 with a large incident angle Φ,thereby causing distortion of a reproduced image in the peripheralregion of the display screen.

Japanese Patent Laid-Open Publication Sho 64-82435 (1989) exemplifies amethod for reducing an incident angle of the electron beam by deflectingthe electron beam electromagnetically once and deflecting it staticallytwice.

With the foregoing example, the electron beam has not only a highacceleration voltage but also a high energy level. Therefore, themagnetic field should be strong enough to cope with such an electronbeam. In addition, a voltage for static deflection should be highenough. Application of the high voltage requires that both theelectromagnetic deflector and the static deflectors should be large. Apower supply for these deflectors would inevitably become large too.Such large apparatuses would consume a large amount of power.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a cathode raytube which can solve the foregoing problems of conventional apparatuses,and can deflect a beam of electrons efficiently by using deflectorsoperable with a low voltage.

According to this invention, a low acceleration voltage is applied to anelectron gun to provide a beam of electrons have a low initial energylevel. An electromagnetic deflector generates a weak magnetic field todeflect the beam of electrons through a sufficient angle. Four staticdeflectors generate magnetic fields to further deflect the beam ofelectrons, so that a path of the beam of electrons can be corrected tobe incident on the fluorescent screen along the normal.

Electric fields generated by the four static deflectors accelerate thebeam of electrons, so that the beam of electrons will be focused ontothe fluorescent screen with a sufficient energy level.

As shown in FIG. 3, the electron beam is easily deflected in a retardingfield b (low electric field). On the other hand, the electron beam isslow to be deflected in accelerating fields a and c (high electricfields). In a field d, the electron beam is scarcely deflected andremains very stable near the fluorescent screen 8.

With this arrangement, the cathode ray tube can minimize the increase ofpower of the deflection yoke, thereby reducing power consumption.

Path analysis of the electron beam is performed by computer simulationaccording to the surface charge method, referred to Chapter 2.5, of thearticle on the electric charge weighing method and surface chargemethod, on pages 44-47, "Electron Beam Handbook", Version 2, publishedby Nikkan Kogyo Shinbunnsha.

The simulation was carried out under the following condition. The targetincident angle θ* is assumed to be less than half the conventionalincident angle (θ* <θ/2), and the target deflection distance d* is morethan the conventional deflection distance d (d*>d).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a cathode ray tube according to anembodiment of this invention;

FIG. 2 shows a path of a beam of electrons in the cathode ray tube ofFIG. 1;

FIG. 3 shows a manner in which the beam of electrons is deflected in theelectric fields;

FIG. 4 shows a relationship between a voltage applied to deflectionelectrodes and orbits of the beam of electrons;

FIG. 5 is a view similar to FIG. 4;

FIG. 6 is a cross-sectional view of a conventional cathode ray tube;

FIG. 7 shows a total length of the cathode ray tube, and a deflectionangle of the electron beam;

FIG. 8 shows a relationship between an applied voltage and a widedeflection angle; and

FIG. 9 shows a relationship between the applied voltage and an incidentangle of the electron beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a cathode ray tube includes first to fourthelectrodes 14 to 17 as well as the components 1 to 8 which are identicalto those of the conventional cathode ray tube shown in FIG. 6. Each ofthe electrodes 14 to 17 has a plurality of electrode elements, andserves as a static deflector electrode. A predetermined voltage isapplied to each electrode via a pin 12 and a lead wire 13, therebyforming an electric field. The electrodes 14 to 17 constitute a staticdeflector.

An acceleration voltage V₀ of the electron gun 4 is set to 5 kV. Thevoltages applied to the first to fourth electrodes 14 to 17 are 5 kV, 30kV, 10 kV and 30 kV, respectively, as the applied voltages V₁, V₂, V₃and V₄. The beam of electrons has a path as shown in FIG. 2.

The electron beam produced by the electron gun 4 has a low accelerationvoltage V₀ as described above. Therefore, the electron beam can bedeflected through a large angle in a weak electric field, so that thestatic deflector can be small in size. The electron beam passing throughthe electromagnetic deflector is accelerated in response to a potentialdifference between the first and second electrodes 14 and 15 (shown at ain FIG. 3). The electron beam is further deflected by the secondelectrode 15, and is somewhat decelerated between the second and thirdelectrodes 15 and 16 (shown at b in FIG. 3). Then, the electron beam isdeflected by the third electrode 16 so as to reduce its deflectionangle. Under this condition, the electron beam has been decelerated at bshown in FIG. 3, being is easily deflected. Therefore, the electron beamcan be deflected even when a low voltage is applied to the thirdelectrode 16. The electron beam is accelerated between the third andfourth electrodes 16 and 17 (shown at c in FIG. 3). Thereafter, theelectron beam is deflected again by the fourth electrode 17, beingfurther accelerated by the voltage applied to the fluorescent screen 8.The electron beam has a sufficient energy level when reaching thefluorescent screen 8.

Under this condition, the electron beam 5 has the deflection distance dand incident angle Φ as shown in TABLE 2.

                  TABLE 2                                                         ______________________________________                                                                    Ratio    Ratio                                    Present   Conven.  Conven.  Present/ Present/                                 invention path 1   path 2   path 1   path 2                                   ______________________________________                                        d   66.92     46.29    66.02  1.45 times                                                                             1.01 times                             Φ                                                                             0.191      0.50     0.20  38.2%    95.5%                                  ______________________________________                                         Present invention: V.sub.0, V.sub.1 = 5 kV, V.sub.2 = 30 kV, V.sub.3 = 10     kV, V.sub.4 = 30 kV                                                           Path 1 V.sub.0, V.sub.1 = 5 kV, V.sub.2 = 30 kV, V.sub.3 = 10 kV, V.sub.4     = 30 kV                                                                       Path 2 V.sub.0, V.sub.1 = 5 kV, V.sub.2 = 60 kV, V.sub.3 = 10 kV, V.sub.4     = 30 kV                                                                  

It is assumed here that a reference voltage H is applied to thefluorescent screen 8. The voltage V₁ applied to the first electrode 14is 20%±20% of H, V₂ to the second electrode 15 is 100%±20% of H, V₃ tothe third electrode 16 is 30%±20% of H, and V₄ to the fourth electrode17 is 100%±20% of H.

When the applied voltages exceed the foregoing values, the electron beam5 collides with the deflector electrode and advances along a path shownby a broken line 25 in FIG. 4 before reaching the fluorescent screen 8.In addition, the electron beam 5 may fail to collide with the targetposition on the fluorescent screen 8 and sometimes advance along a path26 shown in FIG. 5.

TABLE 3 shows the relationship between the applied voltages and thedeflection magnetic fields.

                  TABLE 3                                                         ______________________________________                                        Position                                                                      V.sub.0  V.sub.1                                                                             V.sub.2 V.sub.3                                                                           V.sub.4                                                                             B        Φ                               Unit                                                                          FIG. kV      kV    kV    kV  kV    × 10.sup.4 wb/m.sup.2                                                            rad                               ______________________________________                                        2    5       5     30    10  30    35       0.191                             4    5       5     50    10  30    35       --                                5    5       5     40    10  30    35       -12.0                             ______________________________________                                         Therefore, it is necessary to determine appropriately the voltages applied     to the electrodes to prevent the electron beam from advancing along the     undesired path 25 or 26 as shown in FIG. 4 or 5.

For example, when the voltage to the second electrode is increased, theelectron beam will be further deflected accordingly. However, if theelectron beam is deflected with an angle above the predetermined angle,the electron beam may not reach the fluorescent screen 8. A marginalvalue is shown by a dash-and-dot line in FIG. 8. The voltage applied tothe second electrode 15 has its upper limit determined according to thismarginal value. If the voltage to the fourth electrode 17 is increased,the incident angle Φ will be reduced accordingly. When a voltage abovethe preset value is applied, the incident angle Φ will become negative,thereby offsetting the advantage obtained by a large deflection angle θ.Therefore, the voltage of the fourth electrode is determined to keep theincident angle Φ positive. Experiments were carried out to determine thevoltages to be supplied to the electrodes so that the electron beam doesnot show the paths of FIGS. 4 and 5. It is preferable that each voltageto each electrode should be ±20% of the reference voltage.

In the foregoing embodiment, a monochromatic display tube is describedas an example. However, the tube may be of any other type such as ashadow-mask type.

According to this invention, the beam of electrons can beelectromagnetically deflected in a low electric field. Since theelectron beam is incident onto the fluorescent screen with a small anglecompared with the conventional devices, the electron beam has a smalldeflection angle and will not be distorted in the sectional areathereof. Therefore, the cathode ray tube can assure excellentreproduction of images, and offers a high quality television receiver ata reduced cost.

What is claimed is:
 1. A cathode ray tube comprising:a vacuum tubehaving a panel, a fluorescent surface of said panel, a funnel, anelectron gun for producing a beam of electrons, a single electromagneticdeflector, and a plurality of static deflector means for deflecting andaccelerating said beam of electrons, wherein said beam of electrons isaccelerated by electric fields formed by said plurality of staticdeflectors after said beam of electrons passes through said singleelectromagnetic deflector, wherein voltages applied to each of saidplurality of static deflector means are below a voltage applied to saidfluorescent surface of said panel.
 2. A cathode ray tube comprising:avacuum tube having a panel, a fluorescent surface, a funnel, an electrongun for producing a beam of electrons, a single electromagneticdeflector, and a plurality of static deflector means for deflecting andaccelerating said beam of electrons, wherein said beam of electrons isaccelerated by electric fields formed by said plurality of staticdeflectors after said beam of electrons passes through said singleelectromagnetic detector, wherein said plurality of static deflectormeans includes first through fourth static deflectors, respectivelyarranged in order of an advancing direction of said beam of electrons,said first static deflector generating an electric field in a regionincluding an electromagnetic field generated by said electromagneticdeflector; and said first through fourth static deflectors generate alow electric field, a high electric field, a low electric field, and ahigh electric field, respectively.
 3. The cathode ray tube of claim 2,wherein each of said four static deflectors includes a deflectionelectrode to which a voltage is applied so as to form an electric fieldin a corresponding region of said cathode ray tube.
 4. The cathode raytube of claim 3, wherein the voltages applied to said deflectionelectrodes of said first through fourth deflectors are 20%±20%,100%±20%, 30%±20%, and 100%±20% of the voltage to be applied to saidfluorescent surface, respectively.
 5. A cathode ray tube with reducedpower consumption, comprising:an electron gun, to which a lowacceleration voltage is applied, for generating a low initial energylevel electron beam; electromagnetic deflector means for generating aweak electromagnetic field to deflect the low initial energy level beam;and static deflector means including a plurality of electrodes forapplying an electric field to the electron beam to further deflect,accelerate, and focus the electron beam on a fluorescent screen; whereinthe deflection and acceleration by said static deflector means reducesthe power consumption of said electromagnetic deflector means, andvoltages applied to each of said plurality of static deflector means arebelow a voltage applied to said fluorescent screen.
 6. A cathode raytube with reduced power consumption, comprising:an electron gun, towhich a low acceleration voltage is applied, for generating a lowinitial energy level electron beam; electromagnetic deflector means forgenerating a weak electromagnetic field to deflect the low initialenergy level beam; and static deflector means including a plurality ofelectrodes for applying an electric field to the electron beam tofurther deflect, accelerate, and focus the electron beam on afluorescent screen; wherein the deflection and acceleration by saidstatic deflector means reduces the power consumption of saidelectromagnetic deflector means, said static deflector means includesfirst through fourth static deflectors respectively arranged in order ofan advancing direction of said beam of electrons, and said first staticdeflector generating an electric field in a region including anelectromagnetic field generated by said electromagnetic deflector means,and said first through fourth static deflectors generate a low electricfield, a high electric field, a low electric field, and a high electricfield, respectively.
 7. The cathode ray tube of claim 6, wherein each ofsaid four static deflectors includes a deflection electrode to which avoltage is applied so as to form an electric field in a correspondingregion of said cathode ray tube.
 8. The cathode ray tube of claim 7,wherein the voltage applied to the deflection electrode of the firststatic deflector is less than the voltages applied to the remainingdeflection electrodes.
 9. The cathode ray tube of claim 7, wherein thevoltages applied to said deflection electrodes of said first throughfourth deflectors are 20%±20%, 100%±20%, 30%±20%, and 100%±20% of thevoltage to be applied to said fluorescent screen, respectively.
 10. Amethod of deflecting a beam of electrons onto a fluorescent screenutilizing a cathode ray tube with reduced power consumption, comprisingthe steps of:(a) applying a low acceleration voltage to an electron gun;(b) generating the beam of electrons with a low initial energy levelusing the electron gun; (c) generating a weak electromagnetic field withan electromagnetic deflector for partially deflecting the beam ofelectrons; and (d) applying a plurality of voltages to a plurality ofstatic deflectors to deflect, accelerate, and focus the beam ofelectrons on a fluorescent screen; wherein said steps (a) and (d) reducepower consumption required by said step (c), and the plurality ofapplied voltages are less than a voltage applied to said fluorescentscreen.
 11. A method of deflecting a beam of electrons onto afluorescent screen utilizing a cathode ray tube with reduced powerconsumption, comprising the steps of:(a) applying a low accelerationvoltage to an electron gun; (b) generating the beam of electrons with alow initial energy level using the electron gun; (c) generating a weakelectromagnetic field with an electromagnetic deflector for partiallydeflecting the beam of electrons; and (d) applying a plurality ofvoltages to a plurality of static deflectors to deflect, accelerate, andfocus the beam of electrons on a fluorescent screen; wherein said steps(a) and (d) reduce power consumption required by said step (c), theplurality of applied voltages are applied to first through fourth staticdeflectors respectively arranged in order of an advancing direction ofsaid beam of electrons, said first static deflector generating anelectric field in a region including said weak electromagnetic field,and the first through fourth static deflectors generate a low electricfield, a high electric field, a low electric field, and a high electricfield, respectively.
 12. The method of claim 11, wherein each of thefour static deflectors includes a deflection electrode to which avoltage is applied so as to form an electric field in a correspondingregion of said cathode ray tube.
 13. The method of claim 12, wherein thevoltages applied to the deflection electrodes of said first throughfourth deflectors are 20%±20%, 100%±20%, 30%±20%, and 100%±20% of thevoltage to be applied the said fluorescent screen, respectively.
 14. Themethod of claim 12, wherein the voltage applied to the deflectionelectrode of the first static deflector is less than the voltagesapplied to the remaining deflection electrodes.
 15. A cathode ray tubewith reduced power consumption, comprising:an electron gun, to which alow acceleration voltage is applied, for generating a low initial energylevel electron beam; an electromagnetic deflector generating a weakelectromagnetic field to deflect the low initial energy level beam; andstatic deflector means including a plurality of electrodes havingvoltages applied thereto, for applying an electric field to the electronbeam to further deflect, accelerate, and focus the electron beam on afluorescent screen; said static deflector means reducing the powerconsumption of said electromagnetic deflector though its deflection andacceleration, and the electrode nearest to said electromagneticdeflector has an applied voltage less than the voltages applied to theremaining plurality of electrodes.
 16. A method of deflecting a beam ofelectrons onto a fluorescent screen utilizing a cathode ray tube withreduced power consumption, comprising the steps of:(a) applying a lowacceleration voltage to an electron gun; (b) generating the beam ofelectrons with a low initial energy level using the electron gun; (c)generating a weak electromagnetic field with an electromagneticdeflector for partially deflecting the beam of electrons; and (d)applying a plurality of voltages to a plurality of static deflectors todeflect, accelerate, and focus the beam of electrons on a fluorescentscreen; wherein said steps (a) and (d) reduce power consumption requiredby said step (c), and said step (d) of applying a plurality of voltagesincludes applying a voltage to the static deflector nearest saidelectromagnetic deflector which is less than the voltages applied to theremaining plurality of static deflectors.
 17. A cathode ray tubecomprising:a vacuum tube having a panel, a fluorescent surface, afunnel, an electron gun for producing a beam of electrons with a lowinitial energy level, a single electromagnetic deflector, and aplurality of static deflector means for deflecting, for accelerating andfor increasing the energy level of said beam of electrons, after saidbeam of electrons passes through said single electromagnetic deflectorto the point of impact upon the fluorescent surface.
 18. A method ofdeflecting a beam of electrons onto a fluorescent screen utilizing acathode ray tube with reduced power consumption, comprising the stepsof:(a) applying a low acceleration voltage to an electron gun; (b)generating the beam of electrons with a low initial energy level usingthe electron gun; (c) generating a weak electromagnetic field with anelectromagnetic deflector for partially deflecting the beam ofelectrons; and (d) applying a plurality of voltages to a plurality ofstatic deflectors to deflect, accelerate, and increase the energy levelof the beam of electrons at the point of impact on a fluorescent screento a higher energy level than said low initial energy level.